Ammonium salt of organic acid and resist composition containing the same

ABSTRACT

The present invention provides a novel ammonium salt of an organic acid. When the salt is used as a base additive for a chemically amplified resist, the environmental stability of the resist can be enhanced, and the T-top phenomenon can be effectively prevented. In addition, the line width change caused by acid diffusion can be prevented, and the E 0  value of the resist can be decreased.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to an ammonium salt of an organicacid, and more particularly to a resist composition containing theammonium salt of organic acid.

[0003] 2. Description of the Prior Art

[0004] A chemically amplified resist is a resist whose degree ofdissolution in a developer changes due to the acid generated byexposure. This type of photoresist solution includes a protected resin,a photoacid generator (PAG), and a solvent. The so-called protectedresin is a resin that is protected by an acid-labile protective group.The protective group decomposes in the presence of an acid, thus makingthe resin soluble in an alkali developer.

[0005] When the substrate coated with a chemically amplified resist isexposed to light, the photoacid generator will decompose and generate astrong acid, which will catalyze the resin to induce a catalytichydrolyzation. The protective group (such as an ester group or acetalgroup) in the resin thus decomposes, making the resin soluble in analkali developer. In this way, the degree of dissolution of the resistbefore and after exposure is different, and a pattern can thus beformed.

[0006] When the resist is operated in an environment containing a basematerial, such as hexamethyldisilazane (HMDS) or N-methyl-2-pyrrolidone(NMP), this base material will erode into the surface of the resist.Thus, the acid generated in the exposed area of the resist will beneutralized, which will decrease the concentration of the acid, and theprotective groups can not be completely hydrolyzed. The pattern afterphotolithography thus has adverse phenomenon such as T-top or skin. Inaddition, the acid generated in the exposed area will diffuse into theunexposed area, thus changing the critical dimension (CD).

[0007] To prevent the above problems, either the base concentration inthe environment should be strictly controlled, or a base additive isintroduced to the resist. In the latter case, the resist as a whole isin basic in nature, which can inhibit the resist from absorbing otherbase material present in the environment. When the exposure energy is ashigh as E₀ (dose-to-clear energy), a large amount of photoacid will begenerated after exposure. A small portion of the photoacid isneutralized by the base additive in the exposed area, while most of thephotoacid will catalyze the resin to break the protective groups.Although a small amount of photoacid molecule still goes into theunexposed area through diffusion, the base additive can neutralize thephotoacid in the unexposed area. Therefore, the line width change causedby acid diffusion can be prevented.

[0008] Since the base additive is introduced mainly for reacting withthe photoacid, it is generally called “killer base”. Some researchershave used a primary or secondary amine as a killer base, for example, inU.S. Pat. No. 5,942,367. Such a kind of killer base can effectivelyincrease environmental stability of the resist, and the pattern obtainedis good. However, the primary or secondary amine will react with somecomponents in the resist composition, such as those containing anhydrideor phenol groups. Thus, the storage stability of the resist isdecreased. Some researchers have used a tertiary ammonium salt as akiller base, which is disclosed in, for example, U.S. Pat. Nos.5,633,112 and 5,411,836. However, it is easily seen that the pattern hasa slope problem. Also, the rounding problem occurs due to using only onesalt.

SUMMARY OF THE INVENTION

[0009] Therefore, an object of the present invention is to solve theabove-mentioned problems and to provide an ammonium salt of an organicacid. When the salt is used as a base additive for a chemicallyamplified resist, the environmental stability of the resist can beenhanced, and the T-top phenomenon can be effectively prevented. Inaddition, the line width change caused by acid diffusion can beprevented, and the E₀ value of the resist can be decreased.

[0010] To achieve the above objects, the ammonium salt of an organicacid of the present invention has the following formula:

[0011] wherein

[0012] R is selected from the group consisting of unsubstituted orsubstituted cyclic alkyl, cyclic alkenyl, cyclic ester group, and cyclicketone group having from 3 to 20 carbon atoms,

[0013] R¹, R², and R³ are selected from the group consisting of H,unsubstituted or substituted linear or branched C₁-C₂₀ alkyl, C₃-C₁₀cyclic alkyl, and unsubstituted or substituted linear or branched C₁-C₂₀alkyl containing an N, O, or S atom,

[0014] when R¹, R², and R³ are unsubstituted or substituted linear orbranched C₁-C₂₀ alkyl, any two of R¹, R², R³ can link together to form aring, and when R¹, R², and R³ are unsubstituted or substituted linear orbranched C₁-C₂₀ alkyl containing an N, O, or S atom, any two of R¹, R²,and R³ can link together to form a ring containing N, O, or S,

[0015] n is an integer of from 1 to 4, and

[0016] R¹, R², and R³ are not hydrogen at the same time.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawings,given by way of illustration only and thus not intended to be limitativeof the present invention.

[0018]FIG. 1 is the NMR spectrum of the ammonium salt of organic acid(A) obtained from Example 1 of the present invention.

[0019]FIG. 2 is the NMR spectrum of the ammonium salt of organic acid(B) obtained from Example 2 of the present invention.

[0020]FIG. 3 is the NMR spectrum of the ammonium salt of organic acid(C) obtained from Example 3 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0021] The substituent on R, R¹, R², and R³ of the ammonium salt oforganic acid represented by formula (I) of the present invention can becarboxy, hydroxy, halogen, sulfonyl, ester group, ketone group, ethergroup, or sulfide group.

[0022] In formula (I), when R is unsubstituted or substituted cyclicalkyl or cyclic alkenyl, representative examples include:

[0023] and C₆H₁₄—.

[0024] In the ammonium salt of organic acid of the present invention,representative examples of the ammonium salt portion

[0025] include:

[0026] The method for preparing the ammonium salt of organic acid of thepresent invention is simple. That is, the ammonium salt of organic acidof the present invention can be obtained by reacting a suitable organicacid and a suitable amine in a suitable solvent. Suitable organic acidcan be represented by the formula R—COOH, wherein R is defined as above.Representative examples of organic acids include

[0027] R on the organic acid R—COOH can have other substituents. Whenthe substituent on R is one or more than one carboxy group (—COOH) , theorganic acid thus has two or more than two carboxy groups. Each carboxygroup on the organic acid can react with the amine. Representativeexamples of such organic acids having more than one carboxy groupinclude:

[0028] wherein n is an integer of from 2 to 4.

[0029] The amine suitable for use in the present invention has thefollowing formula:

[0030] wherein R¹, R², and R³ are defined as above.

[0031] Representative examples of amines suitable for use in preparingthe ammonium salt of organic acid of the present invention include:

[0032] In order to make the ammonium salt of organic acid of the presentinvention to be used as a base additive for a resist, particularly achemically amplified resist, preferably, the ammonium salt of organicacid is dissolved in an organic solvent, and has a decompositiontemperature higher than 100° C.

[0033] According to the present invention, the resist compositioncontaining the ammonium salt of organic acid includes the followingcomponents:

[0034] (a) the ammonium salt of organic acid of the present inventionrepresented by formula (I);

[0035] (b) a resin having an acid-labile protective group, wherein theprotective group decomposes in the presence of an acid such that theresin becomes alkaline soluble; and

[0036] (c) a photoacid generator in an amount of 1-20 wt % of the resin(b), wherein the ammonium salt of organic acid (a) is present in anamount of 1-20 mole % of the photoacid generator (c).

[0037] The resist composition of the present invention can furtherinclude component (d) an amine. The amine is optional and not anecessary component. The total amount of components (a) and (d) is 1-20mole % of component (c). The weight ratios of the amine and the ammoniumsalt of organic acid are X:Y, wherein 0≦X≦0.95, 0≦Y≦1, X+Y=1.

[0038] Representative examples of the amines (d) include

[0039] According to the present invention, suitable resin can be anyresin generally used for resists, particularly a resin used for achemically amplified resist. The acid-labile protective group of theresin can be t-butoxy, t-butoxycarbonyloxy (t-BOC), ort-butoxycarbonylmethyl. Suitable resin can be generally apolyhydroxystyrene, in which the hydroxy is substituted with theprotective group. A representative example ispoly-t-butoxycarbonyloxystyrene.

[0040] The photoacid generator suitable for use in the present inventioncan be sulfonium salts, iodonium salts, onium salts, or sulfonates.Representative examples include:

[0041] The resist composition of the present invention is photosensitiveat a wavelength of 150 nm to 600 nm, preferably at a wavelength of 157nm, 193 nm or 248 nm.

[0042] The following examples are intended to illustrate the process andthe advantages of the present invention more fully without limiting itsscope, since numerous modifications and variations will be apparent tothose skilled in the art.

[0043] Preparation of Ammonium Salts of Organic Acid (A)-(C)

EXAMPLE 1

[0044] 2.04 g of dinorbornene carboxylic acid was dissolved in 15 ml ofdichloromethane. After complete dissolution, 3.1 g of1,2,2,6,6-pentamethyl piperidine was added dropwise to the solution. Themixture was stirred for 3 hours. After the reaction was complete, themixture was concentrated under reduced pressure to give a liquidproduct, which was then dried with a vacuum pump to give a pale brownliquid. The liquid was recrystallized with hexane to produce a whitepowder, which was finally dried with a vacuum pump to produce a whitepowder. It was confirmed by the NMR spectrum (FIG. 1) that an ammoniumsalt of an organic acid (A) was successfully prepared.

EXAMPLE 2

[0045] 2.04 g of dinorbornene carboxylic acid was dissolved in 15 ml ofdichloromethane. After complete dissolution, 2.58 g of[1-(2-hydroxyethyl)piperidine] was added dropwise to the solution. Themixture was stirred for 3 hours. After the reaction was complete, themixture was concentrated under reduced pressure to give a liquidproduct, which was then dried with a vacuum pump to give a pale brownliquid. The liquid was recrystallized with hexane, and finally driedwith a vacuum pump to produce a pale brown sticky liquid. It wasconfirmed by the NMR spectrum (FIG. 2) that an ammonium salt of anorganic acid (B) was successfully prepared.

EXAMPLE 3

[0046] 2.22 g of 1,3-adamantane dicarboxylic acid was dissolved in 15 mlof dichloromethane. After complete dissolution, 3.1 g of1,2,2,6,6-pentamethyl piperidine was added dropwise to the solution. Themixture was stirred for 3 hours. After the reaction was complete, themixture was concentrated under reduced pressure to give a liquidproduct, which was then dried with a vacuum pump. It was confirmed byusing the NMR spectrum (FIG. 3) that an ammonium salt of an organic acid(C) was successfully prepared.

[0047] Preparation and Evaluation of Resist Composition

EXAMPLE 4

[0048] 2 g of a copolymer of t-butyl dinorbornene carboxylate, maleicanhydride, 2-methyl-2-norbornyl-acrylate, and2-methyl-norbornyl-norbornene carboxylate (molar ratio=0.1:0.2:0.2:0.1),0.06 g of triphenylsulfonium nonafluorosulfate (PAG; photoacidgenerator), and 0.06 g of t-butyl cholate (dissolution rate inhibitor)were dissolved in 9.15 g of propylene glycol methyl ether acetate(PGMEA) and stirred thoroughly. 1.15 g of the ammonium salt of organicacid (C) obtained from Example 3 (as a killer base) (0.1 wt % in PGMEA)was added to the mixture to obtain a resist composition.

[0049] The resist composition was filtered through a 0.4 μm filter. Thefiltrate was applied to an 8 inch wafer by spin coating at 3000 rpm andsoft baked at 140° C. for 90 seconds. The coated wafer was exposedthrough a mask using 193 nm laser and then baked at 140° C. for 90seconds. The wafer was then developed, rinsed, and dried to form aresist pattern. The dose-to-clear energy (E₀) was 3.90 mJ/cm², and thecontrast value was 15.38.

Comparative Example

[0050] The same procedures were employed as described in Example 4,except that the killer base was replaced by 1.33 g of1-(2-hydroxyethyl)piperidine (0.1 wt % in PGMEA). The coated wafer wasexposed, baked, and developed to form a resist pattern. Thedose-to-clear energy (E₀) was 15.5 mJ/cm².

[0051] The foregoing description of the preferred embodiments of thisinvention has been presented for purposes of illustration anddescription. Obvious modifications or variations are possible in lightof the above teaching. The embodiments chosen and described provide anexcellent illustration of the principles of this invention and itspractical application to thereby enable those skilled in the art toutilize the invention in various embodiments and with variousmodifications as are suited to the particular use contemplated. All suchmodifications and variations are within the scope of the presentinvention as determined by the appended claims when interpreted inaccordance with the breadth to which they are fairly, legally, andequitably entitled.

What is claimed is:
 1. An ammonium salt of an organic acid, having thefollowing formula:

wherein R is selected from the group consisting of unsubstituted orsubstituted cyclic alkyl, cyclic alkenyl, cyclic ester group, and cyclicketone group having from 3 to 20 carbon atoms, R¹,R², and R³ areselected from the group consisting of H, unsubstituted or substitutedlinear or branched C₁-C₂₀ alkyl, C₃-C₁₀ cyclic alkyl, and unsubstitutedor substituted linear or branched C₁-C₂₀ alkyl containing an N, O, or Satom, when R¹, R², and R³ are unsubstituted or substituted linear orbranched C₁-C₂₀ alkyl, any two of R¹, R², R³ can link together to form aring, and when R¹, R², and R³ are unsubstituted or substituted linear orbranched C₁-C₂₀ alkyl containing an N, O, or S atom, any two of R¹, R²,and R³ can link together to form a ring containing N, O, or S, n is aninteger of from 1 to 4, and R¹, R², and R³ are not hydrogen at the sametime.
 2. The ammonium salt of organic acid as claimed in claim 1,wherein the substituent is selected from the group consisting ofcarboxy, hydroxy, halogen, sulfonyl, ester group, ketone group, ethergroup, and sulfide group.
 3. The ammonium salt of organic acid asclaimed in claim 1, wherein the substituent on R is carboxy.
 4. Theammonium salt of organic acid as claimed in claim 1, wherein R isunsubstituted or substituted cyclic alkyl or cyclic alkenyl having from3 to 20 carbon atoms.
 5. The ammonium salt of organic acid as claimed inclaim 4, wherein R is selected from the group consisting of

and C₆H₁₄—.
 6. The ammonium salt of organic acid as claimed in claim 5,wherein R is


7. The ammonium salt of organic acid as claimed in claim 5, wherein R is


8. The ammonium salt of organic acid as claimed in claim 1, wherein theammonium salt portion

is selected from the group consisting of


9. The ammonium salt of organic acid as claimed in claim 8, wherein theammonium salt portion


10. The ammonium salt of organic acid as claimed in claim 8, wherein theammonium salt portion


11. The ammonium salt of organic acid as claimed in claim 1, wherein thesalt can be dissolved in an organic solvent.
 12. The ammonium salt oforganic acid as claimed in claim 1, wherein the salt has a decompositiontemperature higher than 100° C.
 13. A resist composition, comprising thefollowing components: (a) an ammonium salt of an organic acid, havingthe following formula:

 wherein R is selected from the group consisting of unsubstituted orsubstituted cyclic alkyl, cyclic alkenyl, cyclic ester group, and cyclicketone group having from 3 to 20 carbon atoms, R¹, R², and R³ areselected from the group consisting of H, unsubstituted or substitutedlinear or branched C₁-C₂₀ alkyl, C₃-C₁₀ cyclic alkyl, and unsubstitutedor substituted linear or branched C₁-C₂₀ alkyl containing an N, O, or Satom, when R¹, R², and R³ are unsubstituted or substituted linear orbranched C₁-C₂₀ alkyl, any two of R¹, R², R³ can link together to form aring, and when R¹, R², and R³ are unsubstituted or substituted linear orbranched C₁-C₂₀ alkyl containing an N, O, or S atom, any two of R¹, R²,and R³ can link together to form a ring containing N, O, or S, n is aninteger of from 1 to 4, and R¹, R², and R³ are not hydrogen at the sametime; (b) a resin having an acid-labile protective group, wherein theprotective group decomposes in the presence of an acid such that theresin becomes alkaline soluble; and (c) a photoacid generator present inan amount of 1-20 wt % of the resin (b), wherein the ammonium salt oforganic acid (a) is present in an amount of 1-20 mole % of the photoacidgenerator (c).
 14. The resist composition as claimed in claim 13,further comprising (d) an amine, wherein the weight ratios of the amineand the ammonium salt of organic acid are X:Y, wherein 0≦X≦0.95, 0≦Y≦1,X+Y=1, and the total amount of components (a) and (d) is 1-20 mole % ofcomponent (c).
 15. The resist composition as claimed in claim 14,wherein the amine is selected from the group consisting of


16. The resist composition as claimed in claim 13, wherein theacid-labile protective group of the resin is selected from the groupconsisting of t-butoxy, t-butoxycarbonyloxy (t-BOC), andt-butoxycarbonylmethyl.
 17. The resist composition as claimed in claim13, wherein the photoacid generator is selected from the groupconsisting of sulfonium salts, iodonium salts, onium salts, andsulfonates.
 18. The resist composition as claimed in claim 13, whereinthe composition is photosensitive at a wavelength of from 150 nm to 600nm.
 19. The resist composition as claimed in claim 13, wherein thecomposition is photosensitive at wavelengths of 157 nm, 193 nm or 248nm.